ИСТИНА

Osteogenesis of the small and dwarf charr from Lake Davatchan differing in habitats, spawning time, spawning grounds, coloration, meristics, body proportions was studied in laboratory-reared fry. Dwarfs were smaller at hatching; similar developmental stages of skeletal elements occurred in them at smaller size. Differences in the development of teeth, gill rakers, fin rays, pterigyophores, vertebrae were pronounced already in prelarvae (TL 18-20 mm); differences in coloration developed by TL 29-32 mm. In the dwarf and small charr, gill rakers appear at TL~20 and ~ 25 mm, respectively, the increase in their number ceases earlier in dwarfs (at TL~45mm versus >60) mm; scales appear at TL≥49mm and >58mm, respectively. Differences in developmental timing of these two characters are responsible for the main differences between adults of the two forms. Form divergence was presumably driven by differentiation in spawning grounds (hypolymnion and sublitoral zone) and adaptation to two peaks of plankton abundance.